Field of the Invention
This invention relates to loudspeaker assemblies, and, more particularly, to permanent magnet moving coil loudspeaker assemblies.
In a permanent magnet moving coil loudspeaker, a chassis supports the magnet and the moving coil and diaphragm are suspended from the chassis. For many years, the chassis was positioned behind the cone or dome of the loudspeaker. However, as moving coil loudspeakers were used at increasingly higher power, the voice coil heated up rapidly, resulting in a drop in the power output, a reduced longevity, and limitation on power handling. The heat produced by the coil was transferred to the magnet and chassis, but, as the magnet and chassis were located within the speaker cabinet, this did not produce effective dissipation of the heat.
One attempt to meet this problem was to use larger coils, which, thus, increased the area from which heat could be transferred to the magnet and chassis. The increase helped to lower the coil temperature, but, because of their location within the speaker cabinet, the magnet and chassis still received the thermal output from the coil with little or no possibility of them being cooled.
An alternative method of dissipating the heat produced by the coil more efficiently is described in U.S. Pat. No. 5,475,765 to Lyth, in which the chassis is located in front of the diaphragm. The Lyth chassis includes a central hub, an annular outer flange, and spokes extending from the central hub to the flange. The rear of the hub carries the center pole of a ceramic magnet with front and rear suspensions for the diaphragm connected to the chassis. The ceramic magnet includes a center pole and a surrounding ring, with the voice coil movable in the gap between them. The magnet and the voice coil, which is the source of the heat, are both located behind the diaphragm.
U.S. Pat. No. 4,737,992 to Latham-Brown et al. discloses a loudspeaker assembly having a plastic basket with front and rear portions connected to one another. The magnet is disposed in the front portion of the basket and a voice coil assembly is disposed in the interior of the magnet. The diaphragm is connected to the front portion of the basket directly and is also indirectly connected thereto through the spider and the rear portion of the basket. The spider is directly connected to the rear portion of the basket and is indirectly connected to the front portion through the rear portion, through the diaphragm, and through the voice coil and magnet assemblies. The voice coil assembly is also indirectly connected to the front portion of the basket first through spider and rear portion, also through the diaphragm, and finally through the voice coil and magnet assemblies.
With the advent of permanent magnets that use or incorporate neodymium, the problem of heat dissipation has become more important. Neodymium magnets are very high energy magnets, as compared to ceramic magnets. Like ceramic magnets, it is also necessary for neodymium magnets to be kept cool because at typical voice coil operating temperatures the neodymium can demagnetize, resulting in a degradation of performance.